1. Field of the Invention
The invention relates to a circuit and method for displaying battery charge conditions in a portable computer system, and more particularly to a real-time battery gauge display that functions independently of the operating system.
2. Description of the Related Art
Computers are often needed in mobile environments where conventional alternating current power is not available. In such conditions, rechargeable batteries cells are typically used as an alternate source of power. Many acceptable battery technologies exist or are being developed, including nickel-cadmium (NiCd), nickel-metal-hydride (NiMH), lithium ion (Li+) and lithium polymer batteries. These battery cells are capable of providing power to a portable computer system for several hours. The battery cells are incorporated in a battery pack, with the battery cells typically arranged in series fashion. The battery pack is usually recharged in either an external charger or by the power supply of the host computer system.
Despite the mobility allowed by rechargeable batteries, charge cycle life is limited. For this reason, a sensor circuit is often integrated into the battery pack to monitor the voltage of each battery cell and to provide fuel gauging capabilities. Fuel gauging is the process of determining how much useful charge remains in a battery cell or battery pack, and is typically accomplished by Coulomb counting. The sensor circuit typically monitors the battery for undervoltage, overvoltage, overcharge current, and overdischarge current, allowing the battery pack to be accurately charged and discharged.
In what are known as "intelligent" battery packs, the sensor circuit within the pack supplies battery cell information to a battery microcontroller. The microcontroller, in turn, determines whether the battery pack needs to be charged, can be discharged, or is no longer usable. This information can be communicated to the host computer system. A battery pack of this type also includes a charge switch and a discharge switch, controlled by the microcontroller, which enable or disable the charging or discharging of the battery pack according to the state of the battery cells.
In many current portable computers, charge information supplied by the battery microcontroller is converted and displayed on the computer's main video display via a software process. In general, the computer user must take affirmative action to initiate execution of the software process. Although execution of the battery gauge software can be simplified by the use of hot keys or icons, this method of displaying useful battery life suffers from an additional drawback--the portable computer must first be powered-up and the operating system initialized before the software process can be executed. Such a process can be time-consuming for a user merely wishing to ascertain the charge condition of a battery pack.
Some portable systems incorporate a lighted electronic diode (LED) or liquid crystal display (LCD) capable of providing battery charge information. These systems also suffer from practical limitations. A simple LED merely conveys whether a battery pack is capable of powering the computer system. Again, the user must reference a software battery gauge in order to effectively estimate the amount of operating time remaining before battery recharging becomes necessary.
Improved functionality and ease-of-use in the techniques for determining remaining battery life would be desirable.